A novel methanotroph, designated strain HT12(T), was isolated from forest soil in Japan. Cells of strain HT12(T) were Gram-reaction-negative, aerobic, non-motile, coccoid and formed pale-brown colonies. The strain grew only with methane and methanol as sole carbon and energy sources. Cells grew at 5-34 degrees C (optimum 24-32 degrees C). The strain possessed both particulate and soluble methane monooxygenases and assimilated formaldehyde using the ribulose monophosphate pathway. The major cellular fatty acids were C-16:0 (46.9%) and C-14:0 (34.2%), whereas unsaturated C-16 fatty acids, typical of type I methanotrophs, were absent. Comparative 16S rRNA gene sequence analysis showed that the most closely related strains were Methylosoma difficile LC 2(T) (93.1% sequence similarity) and Methylobacter tundripaludum SV96(T) (92.6 % similarity). Phylogenetic analysis based on the pmoA gene indicated that strain HT12(T) formed a distinct lineage within the type I methanotrophs and analysis of the deduced pmoA amino acid sequence of strain HT12(T) showed that it had a 7% divergence from that of its most closely related species. The DNA G+C content was 49.3 mol%. Based on this evidence, strain HT12(T) represents a novel species and genus of the family Methylococcaceae, for which the name Methylovulum miyakonense gen. nov., sp. nov. is proposed. The type strain of the type species is HT12(T) (=NBRC 106162(T) =DSM 23269(T) =ATCC BAA-2070(T)).